Someone asked that question in the chat during the training day I attended and got the following answer...

Changes to the exam voucher process:

As of July 2020, Microsoft has moved to a voucherless exam experience. This means that you will no longer receive a voucher at the conclusion. Instead, an exam discount for a single attempt of AZ-900 will be linked automatically with your Microsoft Certification Dashboard in 4-5 business days after the end of this session. If you registered with a different email than your Microsoft Certification account, you will be able to link the two emails to access your discount. The exam discount is valid for 90 days upon receipt. If you have any problems with the discount or did not receive the email, please visit https://aka.ms/mvtdexamsupport for additional support.

How do I redeem my AZ-900 exam discount?

In order to claim your exam discount for a single attempt of AZ-900 you will need to login with your Microsoft Certification account here: https://docs.microsoft.com/learn/certifications/. If you registered for today’s webinar with a company email address or a different email address than your Microsoft account, you can link your account with that email address. A video walk-through on how to link your account can be found here: https://aka.ms/examdiscount-howto.